Two new systems have been devised that allow the measurements of zero-time values of H+/O ratios during respiratory pulses. This zero-time value, thus far undetermined, is important in understanding the conversion of respiratory to metabolic energy. One system uses mitochondria exposed to substrate and oxygen, but prevented from respiration by a carbon monoxide atmosphere in the dark. A quick exposure to light releases the inhibition and causes a burst of respiration. A microcomputer collects data at 0.01 sec intervals. Computer analysis is used for noise reduction, correction for relaxation times of the electrodes and determination of the time course of the ratio. Results obtained with the system do not support Mitchell's views of energy conversion at sites II abd III of the respiratory chain. A previously undescribed "burst phenomenon" appears to operate in the form of an immediate discharge of a large number of protons per atom of oxygen consumed at zero time. A second system has been developed. This system uses pH and oxygen electrodes placed in a flow cell at fixed distances from a rapid mixing device. The mitochondria are instantly mixed with oxygen in the device and the electrodes continuously sample the suspension at different times of respiration on a scale of milliseconds to 1 sec depending on flow velocities and distance of the electrodes from the point of mixing.